2015 Peterbilt 579 Bulb Sizes

Quick reference

The 2015 Peterbilt 579, a popular choice for long-haul trucking, offers a blend of traditional and modern lighting solutions. While many trucks rolled off the line with conventional halogen bulbs, Peterbilt did offer LED options for certain lighting elements, particularly in the headlights and some rear lighting, often as part of premium trim packages or specific options. It's crucial to verify your truck's original equipment, as upgrading from halogen to LED or vice versa may require different approaches.

For the headlights, the 579 typically utilizes H11 bulbs for the low beams and H9 for the high beams in its halogen configurations. Some premium versions or specific orders might have come equipped with integrated LED headlight assemblies, which are not designed for simple bulb replacement but rather require replacement of the entire assembly if a component fails. Fog lights generally use H10 bulbs. Daytime Running Lights (DRLs) commonly employ 7443 dual-filament bulbs.

Front turn signals often use 3157 or 3457 dual-filament bulbs. Rear turn signals, brake lights, and tail lights frequently share the 3157 bulb size. Many 579s came with traditional halogen 3157 bulbs in the rear, but factory LED tail light assemblies were also available, especially on higher trim levels. Reverse lights are also commonly 3157. License plate lights and side marker lights (both front and rear) typically use the smaller 194 wedge-type bulb, while interior dome and map lights often use a 578 festoon bulb.

LED vs Halogen Upgrade Considerations

Upgrading your 2015 Peterbilt 579 from halogen to LED bulbs can significantly enhance visibility, improve the aesthetic, and reduce power consumption. However, there are several key considerations.

CANBUS Errors

Modern vehicles, including the Peterbilt 579, often incorporate a Controller Area Network Bus (CANBUS) system that monitors electrical circuits, including lighting. Halogen bulbs draw more power than their LED counterparts. When you install an LED bulb, the CANBUS system might detect the lower power draw and interpret it as a burnt-out bulb, triggering a "bulb out" warning on your dashboard or causing hyper-flashing for turn signals. To prevent these CANBUS errors, you will likely need to install CANBUS-compatible LED bulbs or separate load resistors in line with your new LED bulbs. Load resistors mimic the electrical load of a halogen bulb, tricking the CANBUS system into thinking everything is normal.

Adapters Needed

While many LED bulbs are designed for direct plug-and-play replacement of their halogen equivalents, some may require specific adapters or wiring harnesses, especially for headlights or fog lights where the physical size or connection might differ slightly from the OEM bulb. Always ensure the LED bulb you purchase is designed for your specific bulb size (e.g., H11 LED for an H11 halogen socket). For some applications, particularly with aftermarket LED headlights or fog lights that come as full assemblies, additional wiring or splicing might be necessary. It's always recommended to double-check the product specifications and consult the manufacturer's instructions for any recommended adapters or modifications.

How to replace each bulb

Replacing bulbs on your Peterbilt 579 generally involves straightforward procedures, but always allow the bulbs to cool before handling.

• Low Beam/High Beam: Access is typically from behind the headlight assembly, often requiring the removal of a dust cap. Twist the bulb counter-clockwise to remove, unplug the connector, and install the new bulb. Be careful not to touch the glass of new halogen bulbs.
• Fog Light: Usually accessed from underneath the front bumper or by reaching through the wheel well liner. Twist and pull to remove.
• DRL: Often located within the main headlight assembly. Access is typically from the rear, similar to low/high beams.
• Front Turn Signal: Accessed from behind the headlight assembly or by removing screws that hold the turn signal lens.
• Rear Turn Signal/Brake/Tail/Reverse Light: These are usually housed in the same tail light assembly. Access often involves removing screws around the lens or the entire assembly from the rear of the truck. Bulbs typically twist out of their sockets.
• License Plate: Typically involves removing a couple of screws holding the clear lens in place, then simply pulling out the old bulb.
• Side Marker (Front/Rear): Often a simple twist-and-pull socket from the back of the small marker light assembly.
• Dome/Map Light: Carefully pry off the clear plastic lens cover with a plastic trim removal tool or small flathead screwdriver. The festoon bulb usually just clips into place.

Always consult your owner's manual for specific instructions and warnings regarding bulb replacement.

Common lighting issues for this generation

While the 2015 Peterbilt 579 is a reliable truck, several common lighting issues might arise:

• Premature Halogen Bulb Failure: Due to vibration and constant use, halogen bulbs, especially headlights and turn signals, can burn out more frequently than expected. This is normal wear and tear but can be mitigated with higher-quality or long-life halogen replacements, or by upgrading to LEDs.
• Corrosion in Sockets: Exposure to moisture, road salt, and dirt can lead to corrosion in bulb sockets, particularly for exterior lights. This can cause intermittent connections or complete bulb failure. Cleaning the sockets with electrical contact cleaner and applying dielectric grease can help prevent this.
• DRL Malfunctions: Issues with DRLs can sometimes stem from faulty relays, wiring problems, or the multi-function switch. If simple bulb replacement doesn't fix a DRL issue, further electrical diagnosis may be needed.
• Tail Light/Brake Light Assembly Issues: On trucks with integrated LED tail light assemblies, if one or more LEDs fail, the entire assembly typically needs to be replaced, which can be more costly than replacing individual bulbs.
• Flickering Lights or Dim Output: This can often be attributed to poor grounds, low voltage, or faulty wiring harnesses. A thorough inspection of the wiring and electrical system might be necessary.

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